| No | Pattern | Freq | Relations |
|---|---|---|---|
| 1 | [verb] over a period [prep] | 60 |
|
| 2 | [verb] over a period of | 59 |
|
| 3 | [vb past] over a period [prep] | 19 |
|
| 4 | [v-ing] over a period [prep] | 13 |
|
| 5 | [vb -s] over a period [prep] | 8 |
|
| 6 | [vb base] over a period [prep] | 6 |
|
| 7 | [to-vb] over a period [prep] | 6 |
|
| 8 | extend over a period [prep] | 5 |
|
| 9 | [vb infin] over a period [prep] | 5 |
|
| 10 | occur over a period [prep] | 5 |
|
